1. Field of the Invention
The present invention relates to a thin-film magnetic head having at least a magnetoresistive element for reading and a method of manufacturing such a magnetic head, and to a thin-film magnetic head material used for producing a composite thin-film magnetic head having a magnetoresistive element and an induction-type magnetic transducer and a method of manufacturing such a thin-film magnetic head material.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought with an increase in surface recording density of a hard disk drive. A composite thin-film magnetic head has been widely used which is made of a layered structure including a recording head having an induction magnetic transducer for writing and a reproducing head having a magnetoresistive (MR) element for reading. MR elements include an anisotropic magnetoresistive (AMR) element that utilizes the AMR effect and a giant magnetoresistive (GMR) element that utilizes the GMR effect. A reproducing head using an AMR element is called AMR head or simply MR head. A reproducing head using a GMR element is called GMR head. An AMR head is used as a reproducing head whose surface recording density is more than 1 gigabit per square inch. A GMR head is used as a reproducing head whose surface recording density is more than 3 gigabits per square inch.
An AMR head comprises an AMR film having the AMR effect. In place of the AMR film a GMR head comprises a GMR film having the GMR effect. The configuration of the GMR head is similar to that of the AMR head. However, the GMR film exhibits a greater change in resistance under a specific external magnetic field compared to the AMR film. As a result, the reproducing output of the GMR head is about three to five times as great as that of the AMR head.
The MR film may be changed in order to improve the performance of a reproducing head. In general, an AMR film is made of a magnetic substance that exhibits the MR effect and has a single-layer structure. In contrast, many of GMR films have a multilayer structure consisting of a plurality of films. There are several types of mechanisms of producing the GMR effect. The layer structure of a GMR film depends on the mechanism. GMR films include a superlattice GMR film, a granular film, a spin valve film and so on. The spin valve film is most efficient since the film has a relatively simple structure, exhibits a great change in resistance in a low magnetic field, and suitable for mass production. The performance of the reproducing head is thus easily improved by replacing the AMR film with a GMR film and the like with an excellent magnetoresistive sensitivity.
Besides selection of a material as described above, the pattern width such as the MR height, in particular, determines the performance of a reproducing head. The MR height is the length (height) between the end of the MR element closer to the air bearing surface (medium facing surface) and the other end. The MR height is basically controlled by an amount of lapping when the air bearing surface is processed.
Many of reproducing heads have a structure in which the MR element is electrically and magnetically shielded by a magnetic material.
Referring to FIG. 91 to FIG. 100, an example of a manufacturing method of a composite thin-film magnetic head will now be described as an example of a manufacturing method of a related-art thin-film magnetic head. FIGS. 91A to FIG. 98A are cross sections orthogonal to the air bearing surface. FIGS. 91B to FIG. 98B are cross sections parallel to the air bearing surface of the pole portion.
According to the manufacturing method, as shown in FIGS. 91A and 91B, an insulating layer 1102 made of alumina (Al.sub.2 O.sub.3), for example, of about 5 to 10 .mu.m in thickness is deposited on a substrate 1101 made of aluminum oxide and titanium carbide (Al.sub.2 O.sub.3 -TiC), for example. On the insulating layer 1102 a bottom shield layer 1103 made of a magnetic material of 2 to 3 .mu.m in thickness is formed for a reproducing head.
Next, as shown in FIGS. 92A and 92B, on the bottom shield layer 1103 alumina or aluminum nitride, for example, of 50 to 100 nm in thickness is deposited through sputtering to form a bottom shield gap film 1104 as an insulating layer. On the bottom shield gap film 1104 an MR film of tens of nanometers in thickness is formed for making an MR element 1105 for reproduction. Next, on the MR film a photoresist pattern 1106 is selectively formed where the MR element 1105 is to be formed. The photoresist pattern 1106 takes a shape that easily allows lift-off, such as a shape having a T-shaped cross section. Next, with the photoresist pattern 1106 as a mask, the MR film is etched through ion milling to form the MR element 1105. The MR element 1105 may be either a GMR element or an AMR element.
Next, as shown in FIGS. 93A and 93B, on the bottom shield gap film 1104 a pair of first conductive layers 1107 whose thickness is tens of nanometers are formed, using the photoresist pattern 1106 as a mask. The first conductive layers 1107 are electrically connected to the MR element 1105. The first conductive layers 1107 may have a multilayer structure including TiW, CoPt, TiW, and Ta, for example. Next, as shown in FIGS. 94A and 94B, the photoresist pattern 1106 is lifted off. Although not shown in FIGS. 94A and 94B, a pair of second conductive layers whose thickness is 50 to 100 nm are formed in a specific pattern. The second conductive layers are electrically connected to the first conductive layers 1107. The second conductive layers may be made of copper (Cu), for example. The first conductive layers 1107 and the second conductive layers make up leads electrically connected to the MR element 1105.
Next, as shown in FIG. 95A and FIG. 95B, a top shield gap film 1108 of 50 to 150 nm in thickness is formed as an insulating layer on the bottom shield gap film 1104 and the MR film 1105. The MR film 1105 is embedded in the shield gap films 1104 and 1108. Next, on the top shield gap film 1108 a top shield layer-cum-bottom magnetic layer (called top shield layer in the following description) 1109 of about 3 .mu.m in thickness is formed. The top shield layer 1109 is made of a magnetic material and used for both a reproducing head and a recording head.
Next, as shown in FIG. 96A and FIG. 96B, on the top shield layer 1109, a recording gap layer 1110 made of an insulating film such as an alumina film is formed whose thickness is about 0.2 to 0.3 .mu.m. On the recording gap layer 1110 a photoresist layer 1111 for determining the throat height is formed into a specific pattern whose thickness is about 1.0 to 2.0 .mu.m. Next, on the photoresist layer 1111 a thin-film coil 1112 of a first layer is made for the induction-type recording head. The thickness of the thin-film coil 1112 is 3 .mu.m. Next, a photoresist layer 1113 is formed into a specific pattern on the photoresist layer 1111 and the coil 1112. On the photoresist layer 1113 a thin-film coil 1114 of a second layer is then formed into a thickness of 3 .mu.m. Next, a photoresist layer 1115 is formed into a specific pattern on the photoresist layer 1113 and the coil 1114.
Next, as shown in FIG. 97A and FIG. 97B, the recording gap layer 1110 is partially etched in a portion behind the coils 1112 and 1114 (the right side of FIG. 97A) to form a magnetic path. A top pole layer 1116 of about 3 .mu.m in thickness is then formed on the recording gap layer 1110 and the photoresist layers 1111, 1113 and 1115. The top pole layer 1116 is made of a magnetic material for the recording head such as Permalloy (NiFe) or FeN as a high saturation flux density material. The top pole layer 1116 comes to contact with the top shield layer (bottom pole layer) 1109 and is magnetically coupled to the top shield layer 1109 in a portion behind the coils 1112 and 1114.
As shown in FIG. 98A and FIG. 98B, the recording gap layer 1110 and the top shield layer (bottom pole layer) 1109 are etched through ion milling, using the top pole layer 1116 as a mask. Next, an overcoat layer 1117 of alumina, for example, having a thickness of 20 to 30 .mu.m is formed to cover the top pole layer 1116. Finally, machine processing of the slider is performed to form the air bearing surface of the recording head and the reproducing head. The thin-film magnetic head is thus completed. As shown in FIG. 98B, the structure is called trim structure wherein the sidewalls of the top pole layer 1116, the recording gap layer 1110, and part of the top shield layer (bottom pole layer) 1109 are formed vertically in a self-aligned manner. The trim structure suppresses an increase in the effective track width due to expansion of the magnetic flux generated during writing in a narrow track.
FIG. 99 is a top view of the thin-film magnetic head manufactured as described above. The overcoat layer 1117 is omitted in FIG. 99. FIG. 100 is a top view wherein the MR element 1105, the first conductive layer 1107 and the second conductive layer 1118 are formed on the bottom shield gap film 1104. FIG. 91A to FIG. 98A are cross sections taken along line 98A-98A of FIG. 99. FIG. 91B to FIG. 98B are cross sections taken along line 98B--98B of FIG. 99.
As shown in FIG. 99 and FIG. 100, the related-art thin-film magnetic head has the structure wherein the conductive layers 1107 and 1118 connected to the MR element 1105 are inserted in a wide region between the bottom shield layer 1103 and the top shield layer 1109 for shielding the MR element 1105. The very thin bottom shield gap film 1104 and top shield gap film 1108 are each placed between the shield layer 1103 and the conductive layers 1107 and 1118 and between the shield layer 1109 and the conductive layers 1107 and 1118, respectively. High insulation property is therefore required for the shield gap films 1104 and 1108. The yields of the thin-film magnetic heads thus greatly depend on the insulation property.
With improvements in performance of the recording head, a problem of thermal asperity comes up. Thermal asperity is a reduction in reproducing characteristic due to self-heating of the reproducing head during reproduction. To overcome thermal asperity, a material with high cooling efficiency is required for the bottom shield layer 1103 and the shield gap films 1104 and 1108 in the related-art. Therefore, the bottom shield layer 1103 is made of a magnetic material such as Permalloy or Sendust in the related-art. The shield gap films 1104 and 1108 are made of a material such as alumina, through sputtering, into a thickness of 100 to 150 nm, for example. The shield gap films 1104 and 1108 thus magnetically and electrically isolate the shield layers 1103 and 1109 from the MR element 1105 and the conductive layers 1107 and 1118.
It is inevitable that thermal asperity should be overcome in order to improve the performance of the reproducing head. Recently, the thickness of the shield gap films 1104 and 1108 has been reduced to as thin as 50 to 100 nm, for example. The cooling efficiency of the MR element 1105 is thereby improved so as to overcome thermal asperity.
However, since the shield gap films 1104 and 1108 are formed through sputtering, faults may result in the magnetic and electrical insulation that isolates the shield layers 1103 and 1109 from the MR element 1105 and the conductive layers 1107 and 1118, due to particles or pinholes in the films. Such faults more often result if the shield gap films 1104 and 1108 are thinner.
In order to improve the output characteristic of the reproducing head, it is preferred that the wiring resistance of the conductive layer connected to the MR element is as low as possible so that a minute change in the output signal corresponding to a minute change in resistance of the MR element can be detected. Therefore, the area of the conductive layer 1118 is often designed to be large in the related-art. However, the areas of the portions of the conductive layers 1118 that face the shield gap films 1104 and 1108 are made large, as a result. If the shield gap films 1104 and 1108 are thin as described above, magnetic and electrical insulation faults may more often result between the conductive layers 1118 and each of the shield layers 1103 and 1109.
As described above, it is preferred that the wiring resistance of the conductive layers connected to the MR element is low to improve the output characteristic of the reproducing head. However, there is a limit to reducing the wiring resistance of the conductive layers since the conductive layers 1107 and 1118 as thin as 50 to 100 nm are inserted between the shield layers 1103 and 1109 in the related-art thin-film magnetic head.
Since a narrow track width is required for the thin-magnetic head, a minute-size MR element is required. For the GMR head, in particular, it is required to precisely detect the output signal of the minute MR element. It is therefore required to reduce noises caused by internal factors such as the coils of the induction-type recording head or external factors such as the motor of the hard disk drive. However, the conductive layers 1118 carry noises in the related-art thin-film magnetic head. Such noises may reduce the performance of the reproducing head.
In Japanese Patent Application Laid-open Hei 9-312006 (1997) a technique is disclosed for reducing the electric resistance of the lead and preventing insulation faults between the lead and the top shield. The length of the bottom shield is made shorter than the top shield in the direction of drawing out the lead connected to the MR element from between the top and bottom shields. The thickness of the portion of the lead between the top and bottom shields is made thin. The portion of the lead off the bottom shield is made thick and to protrude downward.
In the technique, however, the lead is hardly shielded by the bottom shield. As a result, magnetic flux from the coil is easily received in the GMR head that requires a high output. The lead therefore tends to carry noises.
A technique disclosed in Japanese Patent Application Laid-open Sho 60-93613 (1985) is that a spacer layer is formed on an MR element and contact holes are made in the spacer layer to expose part of the MR element. A shield film and a conductive film (lead) are then formed at the same time, and the conductive film is connected to the MR element through the contact holes.
The technique prevents insulation faults between the conductive film and the shield film. However, the conductive film tends to carry noises since the conductive film is not shielded by the shield film.